recyclerview/recyclerview/src/main/java/androidx/recyclerview/widget/FastScroller.java - platform/frameworks/support - Git at Google

 /*
  * Copyright 2018 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package androidx.recyclerview.widget;

 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.ValueAnimator;
 import android.animation.ValueAnimator.AnimatorUpdateListener;
 import android.graphics.Canvas;
 import android.graphics.drawable.Drawable;
 import android.graphics.drawable.StateListDrawable;
 import android.view.MotionEvent;
 import android.view.View;

 import androidx.annotation.IntDef;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;

 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;

 /**
  * Class responsible to animate and provide a fast scroller.
  */
 class FastScroller extends RecyclerView.ItemDecoration implements RecyclerView.OnItemTouchListener {
     @IntDef({STATE_HIDDEN, STATE_VISIBLE, STATE_DRAGGING})
     @Retention(RetentionPolicy.SOURCE)
     private @interface State { }
     // Scroll thumb not showing
     private static final int STATE_HIDDEN = 0;
     // Scroll thumb visible and moving along with the scrollbar
     private static final int STATE_VISIBLE = 1;
     // Scroll thumb being dragged by user
     private static final int STATE_DRAGGING = 2;

     @IntDef({DRAG_X, DRAG_Y, DRAG_NONE})
     @Retention(RetentionPolicy.SOURCE)
     private @interface DragState{ }
     private static final int DRAG_NONE = 0;
     private static final int DRAG_X = 1;
     private static final int DRAG_Y = 2;

     @IntDef({ANIMATION_STATE_OUT, ANIMATION_STATE_FADING_IN, ANIMATION_STATE_IN,
         ANIMATION_STATE_FADING_OUT})
     @Retention(RetentionPolicy.SOURCE)
     private @interface AnimationState { }
     private static final int ANIMATION_STATE_OUT = 0;
     private static final int ANIMATION_STATE_FADING_IN = 1;
     private static final int ANIMATION_STATE_IN = 2;
     private static final int ANIMATION_STATE_FADING_OUT = 3;

     private static final int SHOW_DURATION_MS = 500;
     private static final int HIDE_DELAY_AFTER_VISIBLE_MS = 1500;
     private static final int HIDE_DELAY_AFTER_DRAGGING_MS = 1200;
     private static final int HIDE_DURATION_MS = 500;
     private static final int SCROLLBAR_FULL_OPAQUE = 255;

     private static final int[] PRESSED_STATE_SET = new int[]{android.R.attr.state_pressed};
     private static final int[] EMPTY_STATE_SET = new int[]{};

     private final int mScrollbarMinimumRange;
     private final int mMargin;

     // Final values for the vertical scroll bar
     @SuppressWarnings("WeakerAccess") /* synthetic access */
     final StateListDrawable mVerticalThumbDrawable;
     @SuppressWarnings("WeakerAccess") /* synthetic access */
     final Drawable mVerticalTrackDrawable;
     private final int mVerticalThumbWidth;
     private final int mVerticalTrackWidth;

     // Final values for the horizontal scroll bar
     private final StateListDrawable mHorizontalThumbDrawable;
     private final Drawable mHorizontalTrackDrawable;
     private final int mHorizontalThumbHeight;
     private final int mHorizontalTrackHeight;

     // Dynamic values for the vertical scroll bar
     @VisibleForTesting int mVerticalThumbHeight;
     @VisibleForTesting int mVerticalThumbCenterY;
     @VisibleForTesting float mVerticalDragY;

     // Dynamic values for the horizontal scroll bar
     @VisibleForTesting int mHorizontalThumbWidth;
     @VisibleForTesting int mHorizontalThumbCenterX;
     @VisibleForTesting float mHorizontalDragX;

     private int mRecyclerViewWidth = 0;
     private int mRecyclerViewHeight = 0;

     private RecyclerView mRecyclerView;
     /**
      * Whether the document is long/wide enough to require scrolling. If not, we don't show the
      * relevant scroller.
      */
     private boolean mNeedVerticalScrollbar = false;
     private boolean mNeedHorizontalScrollbar = false;
     @State private int mState = STATE_HIDDEN;
     @DragState private int mDragState = DRAG_NONE;

     private final int[] mVerticalRange = new int[2];
     private final int[] mHorizontalRange = new int[2];
     @SuppressWarnings("WeakerAccess") /* synthetic access */
     final ValueAnimator mShowHideAnimator = ValueAnimator.ofFloat(0, 1);
     @SuppressWarnings("WeakerAccess") /* synthetic access */
     @AnimationState int mAnimationState = ANIMATION_STATE_OUT;
     private final Runnable mHideRunnable = new Runnable() {
         @Override
         public void run() {
             hide(HIDE_DURATION_MS);
         }
     };
     private final RecyclerView.OnScrollListener
             mOnScrollListener = new RecyclerView.OnScrollListener() {
         @Override
         public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
             updateScrollPosition(recyclerView.computeHorizontalScrollOffset(),
                     recyclerView.computeVerticalScrollOffset());
         }
     };

     FastScroller(RecyclerView recyclerView, StateListDrawable verticalThumbDrawable,
             Drawable verticalTrackDrawable, StateListDrawable horizontalThumbDrawable,
             Drawable horizontalTrackDrawable, int defaultWidth, int scrollbarMinimumRange,
             int margin) {
         mVerticalThumbDrawable = verticalThumbDrawable;
         mVerticalTrackDrawable = verticalTrackDrawable;
         mHorizontalThumbDrawable = horizontalThumbDrawable;
         mHorizontalTrackDrawable = horizontalTrackDrawable;
         mVerticalThumbWidth = Math.max(defaultWidth, verticalThumbDrawable.getIntrinsicWidth());
         mVerticalTrackWidth = Math.max(defaultWidth, verticalTrackDrawable.getIntrinsicWidth());
         mHorizontalThumbHeight = Math
             .max(defaultWidth, horizontalThumbDrawable.getIntrinsicWidth());
         mHorizontalTrackHeight = Math
             .max(defaultWidth, horizontalTrackDrawable.getIntrinsicWidth());
         mScrollbarMinimumRange = scrollbarMinimumRange;
         mMargin = margin;
         mVerticalThumbDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);
         mVerticalTrackDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);

         mShowHideAnimator.addListener(new AnimatorListener());
         mShowHideAnimator.addUpdateListener(new AnimatorUpdater());

         attachToRecyclerView(recyclerView);
     }

     public void attachToRecyclerView(@Nullable RecyclerView recyclerView) {
         if (mRecyclerView == recyclerView) {
             return; // nothing to do
         }
         if (mRecyclerView != null) {
             destroyCallbacks();
         }
         mRecyclerView = recyclerView;
         if (mRecyclerView != null) {
             setupCallbacks();
         }
     }

     private void setupCallbacks() {
         mRecyclerView.addItemDecoration(this);
         mRecyclerView.addOnItemTouchListener(this);
         mRecyclerView.addOnScrollListener(mOnScrollListener);
     }

     private void destroyCallbacks() {
         mRecyclerView.removeItemDecoration(this);
         mRecyclerView.removeOnItemTouchListener(this);
         mRecyclerView.removeOnScrollListener(mOnScrollListener);
         cancelHide();
     }

     @SuppressWarnings("WeakerAccess") /* synthetic access */
     void requestRedraw() {
         mRecyclerView.invalidate();
     }

     void setState(@State int state) {
         if (state == STATE_DRAGGING && mState != STATE_DRAGGING) {
             mVerticalThumbDrawable.setState(PRESSED_STATE_SET);
             cancelHide();
         }

         if (state == STATE_HIDDEN) {
             requestRedraw();
         } else {
             show();
         }

         if (mState == STATE_DRAGGING && state != STATE_DRAGGING) {
             mVerticalThumbDrawable.setState(EMPTY_STATE_SET);
             resetHideDelay(HIDE_DELAY_AFTER_DRAGGING_MS);
         } else if (state == STATE_VISIBLE) {
             resetHideDelay(HIDE_DELAY_AFTER_VISIBLE_MS);
         }
         mState = state;
     }

     private boolean isLayoutRTL() {
         return mRecyclerView.getLayoutDirection() == View.LAYOUT_DIRECTION_RTL;
     }

     public boolean isDragging() {
         return mState == STATE_DRAGGING;
     }

     @VisibleForTesting boolean isVisible() {
         return mState == STATE_VISIBLE;
     }

     public void show() {
         switch (mAnimationState) {
             case ANIMATION_STATE_FADING_OUT:
                 mShowHideAnimator.cancel();
                 // fall through
             case ANIMATION_STATE_OUT:
                 mAnimationState = ANIMATION_STATE_FADING_IN;
                 mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 1);
                 mShowHideAnimator.setDuration(SHOW_DURATION_MS);
                 mShowHideAnimator.setStartDelay(0);
                 mShowHideAnimator.start();
                 break;
         }
     }

     @VisibleForTesting
     void hide(int duration) {
         switch (mAnimationState) {
             case ANIMATION_STATE_FADING_IN:
                 mShowHideAnimator.cancel();
                 // fall through
             case ANIMATION_STATE_IN:
                 mAnimationState = ANIMATION_STATE_FADING_OUT;
                 mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 0);
                 mShowHideAnimator.setDuration(duration);
                 mShowHideAnimator.start();
                 break;
         }
     }

     private void cancelHide() {
         mRecyclerView.removeCallbacks(mHideRunnable);
     }

     private void resetHideDelay(int delay) {
         cancelHide();
         mRecyclerView.postDelayed(mHideRunnable, delay);
     }

     @Override
     public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
         if (mRecyclerViewWidth != mRecyclerView.getWidth()
                 || mRecyclerViewHeight != mRecyclerView.getHeight()) {
             mRecyclerViewWidth = mRecyclerView.getWidth();
             mRecyclerViewHeight = mRecyclerView.getHeight();
             // This is due to the different events ordering when keyboard is opened or
             // retracted vs rotate. Hence to avoid corner cases we just disable the
             // scroller when size changed, and wait until the scroll position is recomputed
             // before showing it back.
             setState(STATE_HIDDEN);
             return;
         }

         if (mAnimationState != ANIMATION_STATE_OUT) {
             if (mNeedVerticalScrollbar) {
                 drawVerticalScrollbar(canvas);
             }
             if (mNeedHorizontalScrollbar) {
                 drawHorizontalScrollbar(canvas);
             }
         }
     }

     private void drawVerticalScrollbar(Canvas canvas) {
         int viewWidth = mRecyclerViewWidth;

         int left = viewWidth - mVerticalThumbWidth;
         int top = mVerticalThumbCenterY - mVerticalThumbHeight / 2;
         mVerticalThumbDrawable.setBounds(0, 0, mVerticalThumbWidth, mVerticalThumbHeight);
         mVerticalTrackDrawable
             .setBounds(0, 0, mVerticalTrackWidth, mRecyclerViewHeight);

         if (isLayoutRTL()) {
             mVerticalTrackDrawable.draw(canvas);
             canvas.translate(mVerticalThumbWidth, top);
             canvas.scale(-1, 1);
             mVerticalThumbDrawable.draw(canvas);
             canvas.scale(-1, 1);
             canvas.translate(-mVerticalThumbWidth, -top);
         } else {
             canvas.translate(left, 0);
             mVerticalTrackDrawable.draw(canvas);
             canvas.translate(0, top);
             mVerticalThumbDrawable.draw(canvas);
             canvas.translate(-left, -top);
         }
     }

     private void drawHorizontalScrollbar(Canvas canvas) {
         int viewHeight = mRecyclerViewHeight;

         int top = viewHeight - mHorizontalThumbHeight;
         int left = mHorizontalThumbCenterX - mHorizontalThumbWidth / 2;
         mHorizontalThumbDrawable.setBounds(0, 0, mHorizontalThumbWidth, mHorizontalThumbHeight);
         mHorizontalTrackDrawable
             .setBounds(0, 0, mRecyclerViewWidth, mHorizontalTrackHeight);

         canvas.translate(0, top);
         mHorizontalTrackDrawable.draw(canvas);
         canvas.translate(left, 0);
         mHorizontalThumbDrawable.draw(canvas);
         canvas.translate(-left, -top);
     }

     /**
      * Notify the scroller of external change of the scroll, e.g. through dragging or flinging on
      * the view itself.
      *
      * @param offsetX The new scroll X offset.
      * @param offsetY The new scroll Y offset.
      */
     void updateScrollPosition(int offsetX, int offsetY) {
         int verticalContentLength = mRecyclerView.computeVerticalScrollRange();
         int verticalVisibleLength = mRecyclerViewHeight;
         mNeedVerticalScrollbar = verticalContentLength - verticalVisibleLength > 0
             && mRecyclerViewHeight >= mScrollbarMinimumRange;

         int horizontalContentLength = mRecyclerView.computeHorizontalScrollRange();
         int horizontalVisibleLength = mRecyclerViewWidth;
         mNeedHorizontalScrollbar = horizontalContentLength - horizontalVisibleLength > 0
             && mRecyclerViewWidth >= mScrollbarMinimumRange;

         if (!mNeedVerticalScrollbar && !mNeedHorizontalScrollbar) {
             if (mState != STATE_HIDDEN) {
                 setState(STATE_HIDDEN);
             }
             return;
         }

         if (mNeedVerticalScrollbar) {
             float middleScreenPos = offsetY + verticalVisibleLength / 2.0f;
             mVerticalThumbCenterY =
                 (int) ((verticalVisibleLength * middleScreenPos) / verticalContentLength);
             mVerticalThumbHeight = Math.min(verticalVisibleLength,
                 (verticalVisibleLength * verticalVisibleLength) / verticalContentLength);
         }

         if (mNeedHorizontalScrollbar) {
             float middleScreenPos = offsetX + horizontalVisibleLength / 2.0f;
             mHorizontalThumbCenterX =
                 (int) ((horizontalVisibleLength * middleScreenPos) / horizontalContentLength);
             mHorizontalThumbWidth = Math.min(horizontalVisibleLength,
                 (horizontalVisibleLength * horizontalVisibleLength) / horizontalContentLength);
         }

         if (mState == STATE_HIDDEN || mState == STATE_VISIBLE) {
             setState(STATE_VISIBLE);
         }
     }

     @Override
     public boolean onInterceptTouchEvent(@NonNull RecyclerView recyclerView,
             @NonNull MotionEvent ev) {
         final boolean handled;
         if (mState == STATE_VISIBLE) {
             boolean insideVerticalThumb = isPointInsideVerticalThumb(ev.getX(), ev.getY());
             boolean insideHorizontalThumb = isPointInsideHorizontalThumb(ev.getX(), ev.getY());
             if (ev.getAction() == MotionEvent.ACTION_DOWN
                     && (insideVerticalThumb || insideHorizontalThumb)) {
                 if (insideHorizontalThumb) {
                     mDragState = DRAG_X;
                     mHorizontalDragX = (int) ev.getX();
                 } else if (insideVerticalThumb) {
                     mDragState = DRAG_Y;
                     mVerticalDragY = (int) ev.getY();
                 }

                 setState(STATE_DRAGGING);
                 handled = true;
             } else {
                 handled = false;
             }
         } else if (mState == STATE_DRAGGING) {
             handled = true;
         } else {
             handled = false;
         }
         return handled;
     }

     @Override
     public void onTouchEvent(@NonNull RecyclerView recyclerView, @NonNull MotionEvent me) {
         if (mState == STATE_HIDDEN) {
             return;
         }

         if (me.getAction() == MotionEvent.ACTION_DOWN) {
             boolean insideVerticalThumb = isPointInsideVerticalThumb(me.getX(), me.getY());
             boolean insideHorizontalThumb = isPointInsideHorizontalThumb(me.getX(), me.getY());
             if (insideVerticalThumb || insideHorizontalThumb) {
                 if (insideHorizontalThumb) {
                     mDragState = DRAG_X;
                     mHorizontalDragX = (int) me.getX();
                 } else if (insideVerticalThumb) {
                     mDragState = DRAG_Y;
                     mVerticalDragY = (int) me.getY();
                 }
                 setState(STATE_DRAGGING);
             }
         } else if (me.getAction() == MotionEvent.ACTION_UP && mState == STATE_DRAGGING) {
             mVerticalDragY = 0;
             mHorizontalDragX = 0;
             setState(STATE_VISIBLE);
             mDragState = DRAG_NONE;
         } else if (me.getAction() == MotionEvent.ACTION_MOVE && mState == STATE_DRAGGING) {
             show();
             if (mDragState == DRAG_X) {
                 horizontalScrollTo(me.getX());
             }
             if (mDragState == DRAG_Y) {
                 verticalScrollTo(me.getY());
             }
         }
     }

     @Override
     public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) { }

     private void verticalScrollTo(float y) {
         final int[] scrollbarRange = getVerticalRange();
         y = Math.max(scrollbarRange[0], Math.min(scrollbarRange[1], y));
         if (Math.abs(mVerticalThumbCenterY - y) < 2) {
             return;
         }
         int scrollingBy = scrollTo(mVerticalDragY, y, scrollbarRange,
                 mRecyclerView.computeVerticalScrollRange(),
                 mRecyclerView.computeVerticalScrollOffset(), mRecyclerViewHeight);
         if (scrollingBy != 0) {
             mRecyclerView.scrollBy(0, scrollingBy);
         }
         mVerticalDragY = y;
     }

     private void horizontalScrollTo(float x) {
         final int[] scrollbarRange = getHorizontalRange();
         x = Math.max(scrollbarRange[0], Math.min(scrollbarRange[1], x));
         if (Math.abs(mHorizontalThumbCenterX - x) < 2) {
             return;
         }

         int scrollingBy = scrollTo(mHorizontalDragX, x, scrollbarRange,
                 mRecyclerView.computeHorizontalScrollRange(),
                 mRecyclerView.computeHorizontalScrollOffset(), mRecyclerViewWidth);
         if (scrollingBy != 0) {
             mRecyclerView.scrollBy(scrollingBy, 0);
         }

         mHorizontalDragX = x;
     }

     private int scrollTo(float oldDragPos, float newDragPos, int[] scrollbarRange, int scrollRange,
             int scrollOffset, int viewLength) {
         int scrollbarLength = scrollbarRange[1] - scrollbarRange[0];
         if (scrollbarLength == 0) {
             return 0;
         }
         float percentage = ((newDragPos - oldDragPos) / (float) scrollbarLength);
         int totalPossibleOffset = scrollRange - viewLength;
         int scrollingBy = (int) (percentage * totalPossibleOffset);
         int absoluteOffset = scrollOffset + scrollingBy;
         if (absoluteOffset < totalPossibleOffset && absoluteOffset >= 0) {
             return scrollingBy;
         } else {
             return 0;
         }
     }

     @VisibleForTesting
     boolean isPointInsideVerticalThumb(float x, float y) {
         return (isLayoutRTL() ? x <= mVerticalThumbWidth
             : x >= mRecyclerViewWidth - mVerticalThumbWidth)
             && y >= mVerticalThumbCenterY - mVerticalThumbHeight / 2
             && y <= mVerticalThumbCenterY + mVerticalThumbHeight / 2;
     }

     @VisibleForTesting
     boolean isPointInsideHorizontalThumb(float x, float y) {
         return (y >= mRecyclerViewHeight - mHorizontalThumbHeight)
             && x >= mHorizontalThumbCenterX - mHorizontalThumbWidth / 2
             && x <= mHorizontalThumbCenterX + mHorizontalThumbWidth / 2;
     }

     @VisibleForTesting
     Drawable getHorizontalTrackDrawable() {
         return mHorizontalTrackDrawable;
     }

     @VisibleForTesting
     Drawable getHorizontalThumbDrawable() {
         return mHorizontalThumbDrawable;
     }

     @VisibleForTesting
     Drawable getVerticalTrackDrawable() {
         return mVerticalTrackDrawable;
     }

     @VisibleForTesting
     Drawable getVerticalThumbDrawable() {
         return mVerticalThumbDrawable;
     }

     /**
      * Gets the (min, max) vertical positions of the vertical scroll bar.
      */
     private int[] getVerticalRange() {
         mVerticalRange[0] = mMargin;
         mVerticalRange[1] = mRecyclerViewHeight - mMargin;
         return mVerticalRange;
     }

     /**
      * Gets the (min, max) horizontal positions of the horizontal scroll bar.
      */
     private int[] getHorizontalRange() {
         mHorizontalRange[0] = mMargin;
         mHorizontalRange[1] = mRecyclerViewWidth - mMargin;
         return mHorizontalRange;
     }

     private class AnimatorListener extends AnimatorListenerAdapter {

         private boolean mCanceled = false;

         AnimatorListener() {
         }

         @Override
         public void onAnimationEnd(Animator animation) {
             // Cancel is always followed by a new directive, so don't update state.
             if (mCanceled) {
                 mCanceled = false;
                 return;
             }
             if ((float) mShowHideAnimator.getAnimatedValue() == 0) {
                 mAnimationState = ANIMATION_STATE_OUT;
                 setState(STATE_HIDDEN);
             } else {
                 mAnimationState = ANIMATION_STATE_IN;
                 requestRedraw();
             }
         }

         @Override
         public void onAnimationCancel(Animator animation) {
             mCanceled = true;
         }
     }

     private class AnimatorUpdater implements AnimatorUpdateListener {
         AnimatorUpdater() {
         }

         @Override
         public void onAnimationUpdate(ValueAnimator valueAnimator) {
             int alpha = (int) (SCROLLBAR_FULL_OPAQUE * ((float) valueAnimator.getAnimatedValue()));
             mVerticalThumbDrawable.setAlpha(alpha);
             mVerticalTrackDrawable.setAlpha(alpha);
             requestRedraw();
         }
     }
 }
	/*
	* Copyright 2018 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package androidx.recyclerview.widget;

	import android.animation.Animator;
	import android.animation.AnimatorListenerAdapter;
	import android.animation.ValueAnimator;
	import android.animation.ValueAnimator.AnimatorUpdateListener;
	import android.graphics.Canvas;
	import android.graphics.drawable.Drawable;
	import android.graphics.drawable.StateListDrawable;
	import android.view.MotionEvent;
	import android.view.View;

	import androidx.annotation.IntDef;
	import androidx.annotation.NonNull;
	import androidx.annotation.Nullable;
	import androidx.annotation.VisibleForTesting;

	import java.lang.annotation.Retention;
	import java.lang.annotation.RetentionPolicy;

	/**
	* Class responsible to animate and provide a fast scroller.
	*/
	class FastScroller extends RecyclerView.ItemDecoration implements RecyclerView.OnItemTouchListener {
	@IntDef({STATE_HIDDEN, STATE_VISIBLE, STATE_DRAGGING})
	@Retention(RetentionPolicy.SOURCE)
	private @interface State { }
	// Scroll thumb not showing
	private static final int STATE_HIDDEN = 0;
	// Scroll thumb visible and moving along with the scrollbar
	private static final int STATE_VISIBLE = 1;
	// Scroll thumb being dragged by user
	private static final int STATE_DRAGGING = 2;

	@IntDef({DRAG_X, DRAG_Y, DRAG_NONE})
	@Retention(RetentionPolicy.SOURCE)
	private @interface DragState{ }
	private static final int DRAG_NONE = 0;
	private static final int DRAG_X = 1;
	private static final int DRAG_Y = 2;

	@IntDef({ANIMATION_STATE_OUT, ANIMATION_STATE_FADING_IN, ANIMATION_STATE_IN,
	ANIMATION_STATE_FADING_OUT})
	@Retention(RetentionPolicy.SOURCE)
	private @interface AnimationState { }
	private static final int ANIMATION_STATE_OUT = 0;
	private static final int ANIMATION_STATE_FADING_IN = 1;
	private static final int ANIMATION_STATE_IN = 2;
	private static final int ANIMATION_STATE_FADING_OUT = 3;

	private static final int SHOW_DURATION_MS = 500;
	private static final int HIDE_DELAY_AFTER_VISIBLE_MS = 1500;
	private static final int HIDE_DELAY_AFTER_DRAGGING_MS = 1200;
	private static final int HIDE_DURATION_MS = 500;
	private static final int SCROLLBAR_FULL_OPAQUE = 255;

	private static final int[] PRESSED_STATE_SET = new int[]{android.R.attr.state_pressed};
	private static final int[] EMPTY_STATE_SET = new int[]{};

	private final int mScrollbarMinimumRange;
	private final int mMargin;

	// Final values for the vertical scroll bar
	@SuppressWarnings("WeakerAccess") /* synthetic access */
	final StateListDrawable mVerticalThumbDrawable;
	@SuppressWarnings("WeakerAccess") /* synthetic access */
	final Drawable mVerticalTrackDrawable;
	private final int mVerticalThumbWidth;
	private final int mVerticalTrackWidth;

	// Final values for the horizontal scroll bar
	private final StateListDrawable mHorizontalThumbDrawable;
	private final Drawable mHorizontalTrackDrawable;
	private final int mHorizontalThumbHeight;
	private final int mHorizontalTrackHeight;

	// Dynamic values for the vertical scroll bar
	@VisibleForTesting int mVerticalThumbHeight;
	@VisibleForTesting int mVerticalThumbCenterY;
	@VisibleForTesting float mVerticalDragY;

	// Dynamic values for the horizontal scroll bar
	@VisibleForTesting int mHorizontalThumbWidth;
	@VisibleForTesting int mHorizontalThumbCenterX;
	@VisibleForTesting float mHorizontalDragX;

	private int mRecyclerViewWidth = 0;
	private int mRecyclerViewHeight = 0;

	private RecyclerView mRecyclerView;
	/**
	* Whether the document is long/wide enough to require scrolling. If not, we don't show the
	* relevant scroller.
	*/
	private boolean mNeedVerticalScrollbar = false;
	private boolean mNeedHorizontalScrollbar = false;
	@State private int mState = STATE_HIDDEN;
	@DragState private int mDragState = DRAG_NONE;

	private final int[] mVerticalRange = new int[2];
	private final int[] mHorizontalRange = new int[2];
	@SuppressWarnings("WeakerAccess") /* synthetic access */
	final ValueAnimator mShowHideAnimator = ValueAnimator.ofFloat(0, 1);
	@SuppressWarnings("WeakerAccess") /* synthetic access */
	@AnimationState int mAnimationState = ANIMATION_STATE_OUT;
	private final Runnable mHideRunnable = new Runnable() {
	@Override
	public void run() {
	hide(HIDE_DURATION_MS);
	}
	};
	private final RecyclerView.OnScrollListener
	mOnScrollListener = new RecyclerView.OnScrollListener() {
	@Override
	public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
	updateScrollPosition(recyclerView.computeHorizontalScrollOffset(),
	recyclerView.computeVerticalScrollOffset());
	}
	};

	FastScroller(RecyclerView recyclerView, StateListDrawable verticalThumbDrawable,
	Drawable verticalTrackDrawable, StateListDrawable horizontalThumbDrawable,
	Drawable horizontalTrackDrawable, int defaultWidth, int scrollbarMinimumRange,
	int margin) {
	mVerticalThumbDrawable = verticalThumbDrawable;
	mVerticalTrackDrawable = verticalTrackDrawable;
	mHorizontalThumbDrawable = horizontalThumbDrawable;
	mHorizontalTrackDrawable = horizontalTrackDrawable;
	mVerticalThumbWidth = Math.max(defaultWidth, verticalThumbDrawable.getIntrinsicWidth());
	mVerticalTrackWidth = Math.max(defaultWidth, verticalTrackDrawable.getIntrinsicWidth());
	mHorizontalThumbHeight = Math
	.max(defaultWidth, horizontalThumbDrawable.getIntrinsicWidth());
	mHorizontalTrackHeight = Math
	.max(defaultWidth, horizontalTrackDrawable.getIntrinsicWidth());
	mScrollbarMinimumRange = scrollbarMinimumRange;
	mMargin = margin;
	mVerticalThumbDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);
	mVerticalTrackDrawable.setAlpha(SCROLLBAR_FULL_OPAQUE);

	mShowHideAnimator.addListener(new AnimatorListener());
	mShowHideAnimator.addUpdateListener(new AnimatorUpdater());

	attachToRecyclerView(recyclerView);
	}

	public void attachToRecyclerView(@Nullable RecyclerView recyclerView) {
	if (mRecyclerView == recyclerView) {
	return; // nothing to do
	}
	if (mRecyclerView != null) {
	destroyCallbacks();
	}
	mRecyclerView = recyclerView;
	if (mRecyclerView != null) {
	setupCallbacks();
	}
	}

	private void setupCallbacks() {
	mRecyclerView.addItemDecoration(this);
	mRecyclerView.addOnItemTouchListener(this);
	mRecyclerView.addOnScrollListener(mOnScrollListener);
	}

	private void destroyCallbacks() {
	mRecyclerView.removeItemDecoration(this);
	mRecyclerView.removeOnItemTouchListener(this);
	mRecyclerView.removeOnScrollListener(mOnScrollListener);
	cancelHide();
	}

	@SuppressWarnings("WeakerAccess") /* synthetic access */
	void requestRedraw() {
	mRecyclerView.invalidate();
	}

	void setState(@State int state) {
	if (state == STATE_DRAGGING && mState != STATE_DRAGGING) {
	mVerticalThumbDrawable.setState(PRESSED_STATE_SET);
	cancelHide();
	}

	if (state == STATE_HIDDEN) {
	requestRedraw();
	} else {
	show();
	}

	if (mState == STATE_DRAGGING && state != STATE_DRAGGING) {
	mVerticalThumbDrawable.setState(EMPTY_STATE_SET);
	resetHideDelay(HIDE_DELAY_AFTER_DRAGGING_MS);
	} else if (state == STATE_VISIBLE) {
	resetHideDelay(HIDE_DELAY_AFTER_VISIBLE_MS);
	}
	mState = state;
	}

	private boolean isLayoutRTL() {
	return mRecyclerView.getLayoutDirection() == View.LAYOUT_DIRECTION_RTL;
	}

	public boolean isDragging() {
	return mState == STATE_DRAGGING;
	}

	@VisibleForTesting boolean isVisible() {
	return mState == STATE_VISIBLE;
	}

	public void show() {
	switch (mAnimationState) {
	case ANIMATION_STATE_FADING_OUT:
	mShowHideAnimator.cancel();
	// fall through
	case ANIMATION_STATE_OUT:
	mAnimationState = ANIMATION_STATE_FADING_IN;
	mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 1);
	mShowHideAnimator.setDuration(SHOW_DURATION_MS);
	mShowHideAnimator.setStartDelay(0);
	mShowHideAnimator.start();
	break;
	}
	}

	@VisibleForTesting
	void hide(int duration) {
	switch (mAnimationState) {
	case ANIMATION_STATE_FADING_IN:
	mShowHideAnimator.cancel();
	// fall through
	case ANIMATION_STATE_IN:
	mAnimationState = ANIMATION_STATE_FADING_OUT;
	mShowHideAnimator.setFloatValues((float) mShowHideAnimator.getAnimatedValue(), 0);
	mShowHideAnimator.setDuration(duration);
	mShowHideAnimator.start();
	break;
	}
	}

	private void cancelHide() {
	mRecyclerView.removeCallbacks(mHideRunnable);
	}

	private void resetHideDelay(int delay) {
	cancelHide();
	mRecyclerView.postDelayed(mHideRunnable, delay);
	}

	@Override
	public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
	if (mRecyclerViewWidth != mRecyclerView.getWidth()
	\|\| mRecyclerViewHeight != mRecyclerView.getHeight()) {
	mRecyclerViewWidth = mRecyclerView.getWidth();
	mRecyclerViewHeight = mRecyclerView.getHeight();
	// This is due to the different events ordering when keyboard is opened or
	// retracted vs rotate. Hence to avoid corner cases we just disable the
	// scroller when size changed, and wait until the scroll position is recomputed
	// before showing it back.
	setState(STATE_HIDDEN);
	return;
	}

	if (mAnimationState != ANIMATION_STATE_OUT) {
	if (mNeedVerticalScrollbar) {
	drawVerticalScrollbar(canvas);
	}
	if (mNeedHorizontalScrollbar) {
	drawHorizontalScrollbar(canvas);
	}
	}
	}

	private void drawVerticalScrollbar(Canvas canvas) {
	int viewWidth = mRecyclerViewWidth;

	int left = viewWidth - mVerticalThumbWidth;
	int top = mVerticalThumbCenterY - mVerticalThumbHeight / 2;
	mVerticalThumbDrawable.setBounds(0, 0, mVerticalThumbWidth, mVerticalThumbHeight);
	mVerticalTrackDrawable
	.setBounds(0, 0, mVerticalTrackWidth, mRecyclerViewHeight);

	if (isLayoutRTL()) {
	mVerticalTrackDrawable.draw(canvas);
	canvas.translate(mVerticalThumbWidth, top);
	canvas.scale(-1, 1);
	mVerticalThumbDrawable.draw(canvas);
	canvas.scale(-1, 1);
	canvas.translate(-mVerticalThumbWidth, -top);
	} else {
	canvas.translate(left, 0);
	mVerticalTrackDrawable.draw(canvas);
	canvas.translate(0, top);
	mVerticalThumbDrawable.draw(canvas);
	canvas.translate(-left, -top);
	}
	}

	private void drawHorizontalScrollbar(Canvas canvas) {
	int viewHeight = mRecyclerViewHeight;

	int top = viewHeight - mHorizontalThumbHeight;
	int left = mHorizontalThumbCenterX - mHorizontalThumbWidth / 2;
	mHorizontalThumbDrawable.setBounds(0, 0, mHorizontalThumbWidth, mHorizontalThumbHeight);
	mHorizontalTrackDrawable
	.setBounds(0, 0, mRecyclerViewWidth, mHorizontalTrackHeight);

	canvas.translate(0, top);
	mHorizontalTrackDrawable.draw(canvas);
	canvas.translate(left, 0);
	mHorizontalThumbDrawable.draw(canvas);
	canvas.translate(-left, -top);
	}

	/**
	* Notify the scroller of external change of the scroll, e.g. through dragging or flinging on
	* the view itself.
	*
	* @param offsetX The new scroll X offset.
	* @param offsetY The new scroll Y offset.
	*/
	void updateScrollPosition(int offsetX, int offsetY) {
	int verticalContentLength = mRecyclerView.computeVerticalScrollRange();
	int verticalVisibleLength = mRecyclerViewHeight;
	mNeedVerticalScrollbar = verticalContentLength - verticalVisibleLength > 0
	&& mRecyclerViewHeight >= mScrollbarMinimumRange;

	int horizontalContentLength = mRecyclerView.computeHorizontalScrollRange();
	int horizontalVisibleLength = mRecyclerViewWidth;
	mNeedHorizontalScrollbar = horizontalContentLength - horizontalVisibleLength > 0
	&& mRecyclerViewWidth >= mScrollbarMinimumRange;

	if (!mNeedVerticalScrollbar && !mNeedHorizontalScrollbar) {
	if (mState != STATE_HIDDEN) {
	setState(STATE_HIDDEN);
	}
	return;
	}

	if (mNeedVerticalScrollbar) {
	float middleScreenPos = offsetY + verticalVisibleLength / 2.0f;
	mVerticalThumbCenterY =
	(int) ((verticalVisibleLength * middleScreenPos) / verticalContentLength);
	mVerticalThumbHeight = Math.min(verticalVisibleLength,
	(verticalVisibleLength * verticalVisibleLength) / verticalContentLength);
	}

	if (mNeedHorizontalScrollbar) {
	float middleScreenPos = offsetX + horizontalVisibleLength / 2.0f;
	mHorizontalThumbCenterX =
	(int) ((horizontalVisibleLength * middleScreenPos) / horizontalContentLength);
	mHorizontalThumbWidth = Math.min(horizontalVisibleLength,
	(horizontalVisibleLength * horizontalVisibleLength) / horizontalContentLength);
	}

	if (mState == STATE_HIDDEN \|\| mState == STATE_VISIBLE) {
	setState(STATE_VISIBLE);
	}
	}

	@Override
	public boolean onInterceptTouchEvent(@NonNull RecyclerView recyclerView,
	@NonNull MotionEvent ev) {
	final boolean handled;
	if (mState == STATE_VISIBLE) {
	boolean insideVerticalThumb = isPointInsideVerticalThumb(ev.getX(), ev.getY());
	boolean insideHorizontalThumb = isPointInsideHorizontalThumb(ev.getX(), ev.getY());
	if (ev.getAction() == MotionEvent.ACTION_DOWN
	&& (insideVerticalThumb \|\| insideHorizontalThumb)) {
	if (insideHorizontalThumb) {
	mDragState = DRAG_X;
	mHorizontalDragX = (int) ev.getX();
	} else if (insideVerticalThumb) {
	mDragState = DRAG_Y;
	mVerticalDragY = (int) ev.getY();
	}

	setState(STATE_DRAGGING);
	handled = true;
	} else {
	handled = false;
	}
	} else if (mState == STATE_DRAGGING) {
	handled = true;
	} else {
	handled = false;
	}
	return handled;
	}

	@Override
	public void onTouchEvent(@NonNull RecyclerView recyclerView, @NonNull MotionEvent me) {
	if (mState == STATE_HIDDEN) {
	return;
	}

	if (me.getAction() == MotionEvent.ACTION_DOWN) {
	boolean insideVerticalThumb = isPointInsideVerticalThumb(me.getX(), me.getY());
	boolean insideHorizontalThumb = isPointInsideHorizontalThumb(me.getX(), me.getY());
	if (insideVerticalThumb \|\| insideHorizontalThumb) {
	if (insideHorizontalThumb) {
	mDragState = DRAG_X;
	mHorizontalDragX = (int) me.getX();
	} else if (insideVerticalThumb) {
	mDragState = DRAG_Y;
	mVerticalDragY = (int) me.getY();
	}
	setState(STATE_DRAGGING);
	}
	} else if (me.getAction() == MotionEvent.ACTION_UP && mState == STATE_DRAGGING) {
	mVerticalDragY = 0;
	mHorizontalDragX = 0;
	setState(STATE_VISIBLE);
	mDragState = DRAG_NONE;
	} else if (me.getAction() == MotionEvent.ACTION_MOVE && mState == STATE_DRAGGING) {
	show();
	if (mDragState == DRAG_X) {
	horizontalScrollTo(me.getX());
	}
	if (mDragState == DRAG_Y) {
	verticalScrollTo(me.getY());
	}
	}
	}

	@Override
	public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) { }

	private void verticalScrollTo(float y) {
	final int[] scrollbarRange = getVerticalRange();
	y = Math.max(scrollbarRange[0], Math.min(scrollbarRange[1], y));
	if (Math.abs(mVerticalThumbCenterY - y) < 2) {
	return;
	}
	int scrollingBy = scrollTo(mVerticalDragY, y, scrollbarRange,
	mRecyclerView.computeVerticalScrollRange(),
	mRecyclerView.computeVerticalScrollOffset(), mRecyclerViewHeight);
	if (scrollingBy != 0) {
	mRecyclerView.scrollBy(0, scrollingBy);
	}
	mVerticalDragY = y;
	}

	private void horizontalScrollTo(float x) {
	final int[] scrollbarRange = getHorizontalRange();
	x = Math.max(scrollbarRange[0], Math.min(scrollbarRange[1], x));
	if (Math.abs(mHorizontalThumbCenterX - x) < 2) {
	return;
	}

	int scrollingBy = scrollTo(mHorizontalDragX, x, scrollbarRange,
	mRecyclerView.computeHorizontalScrollRange(),
	mRecyclerView.computeHorizontalScrollOffset(), mRecyclerViewWidth);
	if (scrollingBy != 0) {
	mRecyclerView.scrollBy(scrollingBy, 0);
	}

	mHorizontalDragX = x;
	}

	private int scrollTo(float oldDragPos, float newDragPos, int[] scrollbarRange, int scrollRange,
	int scrollOffset, int viewLength) {
	int scrollbarLength = scrollbarRange[1] - scrollbarRange[0];
	if (scrollbarLength == 0) {
	return 0;
	}
	float percentage = ((newDragPos - oldDragPos) / (float) scrollbarLength);
	int totalPossibleOffset = scrollRange - viewLength;
	int scrollingBy = (int) (percentage * totalPossibleOffset);
	int absoluteOffset = scrollOffset + scrollingBy;
	if (absoluteOffset < totalPossibleOffset && absoluteOffset >= 0) {
	return scrollingBy;
	} else {
	return 0;
	}
	}

	@VisibleForTesting
	boolean isPointInsideVerticalThumb(float x, float y) {
	return (isLayoutRTL() ? x <= mVerticalThumbWidth
	: x >= mRecyclerViewWidth - mVerticalThumbWidth)
	&& y >= mVerticalThumbCenterY - mVerticalThumbHeight / 2
	&& y <= mVerticalThumbCenterY + mVerticalThumbHeight / 2;
	}

	@VisibleForTesting
	boolean isPointInsideHorizontalThumb(float x, float y) {
	return (y >= mRecyclerViewHeight - mHorizontalThumbHeight)
	&& x >= mHorizontalThumbCenterX - mHorizontalThumbWidth / 2
	&& x <= mHorizontalThumbCenterX + mHorizontalThumbWidth / 2;
	}

	@VisibleForTesting
	Drawable getHorizontalTrackDrawable() {
	return mHorizontalTrackDrawable;
	}

	@VisibleForTesting
	Drawable getHorizontalThumbDrawable() {
	return mHorizontalThumbDrawable;
	}

	@VisibleForTesting
	Drawable getVerticalTrackDrawable() {
	return mVerticalTrackDrawable;
	}

	@VisibleForTesting
	Drawable getVerticalThumbDrawable() {
	return mVerticalThumbDrawable;
	}

	/**
	* Gets the (min, max) vertical positions of the vertical scroll bar.
	*/
	private int[] getVerticalRange() {
	mVerticalRange[0] = mMargin;
	mVerticalRange[1] = mRecyclerViewHeight - mMargin;
	return mVerticalRange;
	}

	/**
	* Gets the (min, max) horizontal positions of the horizontal scroll bar.
	*/
	private int[] getHorizontalRange() {
	mHorizontalRange[0] = mMargin;
	mHorizontalRange[1] = mRecyclerViewWidth - mMargin;
	return mHorizontalRange;
	}

	private class AnimatorListener extends AnimatorListenerAdapter {

	private boolean mCanceled = false;

	AnimatorListener() {
	}

	@Override
	public void onAnimationEnd(Animator animation) {
	// Cancel is always followed by a new directive, so don't update state.
	if (mCanceled) {
	mCanceled = false;
	return;
	}
	if ((float) mShowHideAnimator.getAnimatedValue() == 0) {
	mAnimationState = ANIMATION_STATE_OUT;
	setState(STATE_HIDDEN);
	} else {
	mAnimationState = ANIMATION_STATE_IN;
	requestRedraw();
	}
	}

	@Override
	public void onAnimationCancel(Animator animation) {
	mCanceled = true;
	}
	}

	private class AnimatorUpdater implements AnimatorUpdateListener {
	AnimatorUpdater() {
	}

	@Override
	public void onAnimationUpdate(ValueAnimator valueAnimator) {
	int alpha = (int) (SCROLLBAR_FULL_OPAQUE * ((float) valueAnimator.getAnimatedValue()));
	mVerticalThumbDrawable.setAlpha(alpha);
	mVerticalTrackDrawable.setAlpha(alpha);
	requestRedraw();
	}
	}
	}